library/GSM_RR_Types.ttcn: fix 'presence' in tr_PacketUlSglAssign

According to 3GPP TS 44.018, section 10.5.2.16 "IA Rest Octets",
the first bit of Packet Uplink Assignment defines whether it is
a dynamic (1) or single block (0) allocation.

Change-Id: If2bee9b1b065fcfedd0e57a6487040cefe2e50c5
diff --git a/library/GSM_RR_Types.ttcn b/library/GSM_RR_Types.ttcn
index 70009ac..7351cdf 100644
--- a/library/GSM_RR_Types.ttcn
+++ b/library/GSM_RR_Types.ttcn
@@ -805,7 +805,7 @@
 	};
 
 	template PacketUlAssign tr_PacketUlSglAssign := {
-		presence := '1'B, /* Single Block Assignment */
+		presence := '0'B, /* Single Block Assignment */
 		dynamic := omit,
 		single := {
 			alpha_present := ?,